1. Technical Field
This invention is related to the field of memory implementation, and more particularly to sensing techniques.
2. Description of the Related Art
Memories typically include a number of data storage cells composed of interconnected transistors fabricated on a semiconductor substrate. Such data storage cells may be constructed according to a number of different circuit design styles. For example, the data storage cells may be implemented as a single transistor coupled to a capacitor to form a dynamic storage cell. Alternatively, cross-couple inverters may be employed to form a static storage cell, or a floating gate MOSFET may be used to create a non-volatile storage cell.
During the semiconductor manufacturing process, variations in lithography, transistor dopant levels, etc., may result in different electrical characteristics between storage cells that are intended to have identical characteristics. Additional variation in electrical characteristics may occur due to aging effects within the transistors as the device is repeatedly operated. These differences in electrical characteristics between transistors can result in data storage cells that output different small signal voltages for the same stored data.
In some cases, the variation of a given data storage cell may result in an output voltage that cannot be properly amplified by the sense amplifier. Such data storage cells may be identified as hard failures during initial testing which may require replacement with redundant data storage cells in order to achieve manufacturing yield goals.